Industrial applications in this field require cables to cross generally metallic walls, the cables carrying high-voltage currents which furthermore may be high-current pulses, (for instance 10,000 amperes) of a width of a microsecond.
A particular problem arises when a transition must be carried out between an insulated coaxial line on one side of the wall to a line which is uninsulated relative to air on the other side of the wall.
Several designs already have been developed in this field.
Conventional products such as those commercially offered by high-voltage connector specialized manufacturers and known under Trademarks RADIALL®, ALCATEL®, ETAT®, LEYBOLD®, PFFEIFER®, VARIAN® or VEECO®, which in general consist of a socket affixed to the wall for being hooked to a connector at the end of the coaxial line. To prevent electrical breakdown between the end commonly called the hot point of the line and the metal wall, the connector consists at the air-side line of an insulator shaped in such a corrugated way that the surface distance between these two elements shall be adequate, i.e., increasing the distance between the hot point and the wall allows increasing the paths of the electric paths in case of breakdowns.
Moreover, and obviously as regards the geometry of such aforementioned connectors, they are deprived of shielding around the insulation portion of the air-side line, in order to avoid electrical breakdown. As a result electromagnetic shielding stops where the coaxial cable is hooked up to the socket.
Another design creates dielectric continuity by inserting grease or oil between the socket's insulator and the metal wall in order to enhance dielectric strength while averting any air pocket between these various elements. As a result surface breakdowns take place at the insulators' joint and along them are minimized because the air pockets between the various materials were eliminated. The maximum increase in voltage strength attained in such manner however is only 20%.
On the other hand the practical implementation of these electric insulation procedures incurs many drawbacks, in particular when connectors shall service high voltage generators and especially when such generators shall generate narrow pulses.
The shape effect of the socket insulators most often entails bulk. The substantially bulky insulators of these sockets entail excessive inductance that may degrade the performance of such high-voltage generators.
The lack of shielding of the insulating part of the air-side liner is especially problematic when transmitting current pulses with steep leading edges because a significant length of unshielded line with voltage applied to it entails back emf's hampering the currents at high frequencies. The losses caused by the back emf's in such cases may render conventional connectors impractical.
Again a number of drawbacks are incurred when using oil or grease impregnated insulating materials: if the temperature is too low, some oils will gel or crystallize. Also high currents which generate electric arcing between the conductors and micro-discharges near the dielectrics will pollute the oil films, in particular by catalyzing some oil hydrolysis. Once they acquire moisture, the greases and oils lose dielectric strength. Again all these designs are bulky and cannot be used with small generators.
The objective of the invention is palliation by creating a wall feedthrough preserving shielding protection as far as the transit through the wall, the feedthrough part which emerges beyond the wall being small (usually less than a cm even for voltages of about 100 kv).
Another object of the present invention is a hookup device for high-voltage cables and designed on the same principles as the wall feedthrough.
Accordingly, the objective of the present invention is a wall feedthrough in particular for a metal wall and for a high-voltage coaxial cable, the feedthrough comprising an insulating socket affixed to the wall. This socket exhibits an upstream end (conventionally denoting the side of air-side transmission line) and a downstream end (conventionally denoting the side of the insulated transmission line), each end projecting from its side of the wall, the inner cable conductor being continuously passing through the insulating socket. This feedthrough also includes primary mechanical fasteners which shall cooperate with secondary mechanical fasteners affixed to the cable's sheath.